Coating system for flexible extrusions

ABSTRACT

A sealing system for automotives comprising a coating formulation applied to a flexible thermoplastics extrusion wherein the coating formulation comprises a UV curable resin.

The present invention is concerned with coating systems for flexibleextrusions, specifically thermoplastics extrusions which are used asseals, for example, in the automotive industry.

Automotive sealing systems are manufactured from a range of syntheticrubbers and manufactured thermoplastic materials, generally byextrusion. The most common synthetic rubber is EPDM (Ethylene PropyleneDiene Monomer) while the thermoplastics tend to be ThermoplasticElastomers (TPEs), Thermoplastic Olefins (TPOs) or ThermoplasticVulcanisate (CPVs). Whether they are to form glass-run channels,weatherstrip or belt-line seals, they all require a coating to beapplied to their surface in order to improve the mechanical, chemicaland physical properties of the seal.

Presently, the coating systems used are based upon polyester flocculatedfibres, polyurethane or silicone resin systems or combinations thereof.The polyester flocculated fibres are bonded to the seal surface by meansof a heat-activated adhesive.

The polyurethane and silicone resin materials can be dispersions and/orsolutions in deionised water or organic solvent blends. These resins aretypically crosslinked, usually employing isocyanate monomers to developthe physical and mechanical properties of the cured coatings.

The lubricant species utilised within the present coatings are primarilyeither PTFE (PolyTetraFluoroEthylene) or silicone, supplied indispersion, solution or micropowder form.

The coating formulations are applied by conventional spray, brushing,wiping and dipping techniques. The cure activation mechanism is physicalheating of the seal component via combinations of either hot air, IR(light frequency) and or UHF (particle frequency), and is provided bytunnel ovens, of between 10 to 40 metres in length. The cure time forthese existing coating systems are typically between 1 and 15 minutes,depending upon the oven facilities available.

It is an object of the present invention to provide a coating system fora flexible extrusion which does not require a long curing time and whichcan therefore avoid the use of lengthy tunnel ovens.

According to the invention, there is provided a coating formulation fora flexible thermoplastic extrusion, the coating formulation whichcomprises a curable resin and optionally, a solvent or dispersant forthe resin, and in which the resin is a UV curable resin. Preferably theresin is a PUD (polyurethane dispersion) and the solvent/dispersant iswater. The formulation preferably includes a photoinitiator, across-linking agent and preferably also a friction-reducing agent.

Preferably the PUD is a aliphatic waterborne resin or a mixture of suchresins.

Examples include Neorad R440, Neorez R600 of which a mixture of both isparticularly preferred.

Suitable photoinitiators include Irgacure 184 and others. A preferredphotoinitiator might be1-[4-(2-Hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one(Irgacure 2959). This cross-linking agent activates the cross-linking ofthe PUD dispersion when, exposed to UV light of 200-400 nm (UVA, UVB andUVC) to form a dry, flexible film bonding it to the substrate.

The friction-reducing agent is preferably PTFE, which is preferably inthe form of a micropowder which has an average particle size of 8 μm. Aparticularly preferred friction-reducing agent is Fomblin FE20 EG, anaqueous microemulsion based on perfluoropolyether.

The formulation may also include one or more wetting agents, surfactantsand pigments. Suitable wetting agents include i.) Silicone polyesteracrylate Tegorad 2200N, Slip and Flow additive, ii.) Polyether siloxanecopolymer Tegoglide 450.

Suitable surfactants include FC430, Zonyl FSG, Tinuvin 292, Tinuvin 1130and Tinuvin 144.

The PUD may represent from 40 to 80 wt %, preferably 60 to 80 wt %, morepreferably 40 wt % of the formulation, excluding the solvent/dispersant.

The photoinitiator may represent 1 to 5 wt %, preferably 3 to 5 wt %,more preferably 3 wt % of the formulation, excluding thesolvent/dispersant.

The friction reducing agent may represent 5 to 30 wt %, preferably 10 to25 wt %, more preferably 10 wt % of the formulation, excluding thesolvent/dispersant.

The PUD may be present in the solvent/dispersant in a concentration offrom 38 to 32 wt %, preferably 40 to 41 wt %, for example NeoRad R440 orNeoRez R600 (aliphatic waterborne urethanes manufactured by NeoResins)of which a mixture of both is particularly preferred.

The formulation may be applied to the extruded product continuously, onextrusion, or may be applied to the product after forming to shape. Itmay be applied by any suitable method, eg. by application by hand sprayand automated spray application, brushing, wiping, dipping.

Suitable UV sources included WVA 315400 nm, UVB 280-315 nm, WVC 200-280nm. A preferred source is UV A, B, C. Curing of the resin may take from1 to 2 seconds but typically, full curing may take less than 1 second.Furthermore, curing may be effected at ambient temperatures. Thus thesystem of the invention substantially reduces the cure oven length andcure time and allows the formation of a tough, flexible, low frictionfilm by curing the coating in <1 second, compared to traditional curingrequirements of 1-15 mins@ between 150-180° C. The coating may havecoefficient of dynamic friction value <0.9, and a coefficient of staticfriction value <0.9, and its properties include good solvent resistance,flexibility, water resistance, freeze-release properties, heat andhumidity resistance. It may be applied to extruded profiles made fromThermoplastic Elastomers (TPE), Thermoplastic olefins (TPO) andThermoplastic Vulcanisates (TPV). Preferably, the coating is applied toa TPE extruded substrate.

In a particularly preferred form, the invention provides a formulationwhich combines the use of a perfluropolyether with a UV curablewaterborne PUD resin based system, suitable for application by spraying,brushing, wiping, dipping etc., that, when applied onto theaforementioned substrates, offers a flexible film with elasticityof >100%, preferably 120% or even 150%, in extension, whilst retainingthe mechanical and chemical resistant properties outlined above. Incontrast, existing UV cured coatings are limited to applications whereelasticity of the coating film is not required, and in many casesavoided. The present invention is capable of formulating a tough, buthighly flexible UV cured coating having repeatable flexibility forapplication on dynamic sealing systems applications, across a wide rangeof substrates.

In a preferred embodiment, the present invention provides a coatingformulation which has application in sealing systems where the aim is toprovide a seal having a coating which retains its flexibilty throughrepeated flexing and deformation of the seal. This high degree ofrepeatable flexibility of the coating is of particular importance in“weatherstrip” seals, which include, inter alia, automotive door, bonnet(hood) and boot (trunk) seals, that are exposed to repeated structuralcompression and release.

The present invention exhibits various further advantages. As continuingenvironmental assessments are forcing lower VOC limits, the TV coatingsof the present invention have low or zero solvent emissions, either byusing water as the solvent/dispersant or by using a 100% monomer system.

The formulation can be provided as a 1-pack spray applied system, whichhas increased pot-life compared to a 2 pack cross-linked coating, asused in prior art systems. Online set up waste is greatly reduced,coating inspection/thickness measurement can be measured seconds aftercuring compared to 3 minutes curing time for conventional curing,greatly reducing coating and substrate waste.

Smaller production facilities are required. Current state of the artsystems employ tunnel ovens with a typical length of between 10 and 40metres. The present invention requires a two metre long enclosed lightsource, thereby reducing extrusion line lengths by a factor of, atleast, 5. The system may also result in lower energy costs compared toconvention, IR or microwave curing ovens. New equipment can easily befitted to existing production lines.

The recent increase in environmental awareness has resulted in a trendtowards a greater use of recyclable materials. This trend isparticularly evident in the automotive industry where there is pressurebeing placed on manufacturers to replace rubber and plasticsapplications with recyclable materials. The present invention provides afurther advantage in that the coating formulations have application inthe coating of thermoplastic materials which can be recycled.

The invention may also allow increased use of TPE's, polymers whichcombine the service properties of elastomers with the processingproperties of thermoplastics, as the substrate material in the future.These include:

-   i.) Blends of rubbers with thermoplastics (EPDM and Polypropylene    (PP) and Natural rubber/Polypropylene (NR/PP))-   ii.) Soft block copolymers-   iii.) Hard block copolymers

Temperature sensitive materials such as TpEs, TpVs and TPOs require lowtemperature curing at about 100° C. to prevent distortion of theirsurface or mechanical properties. This is presently achieved by using acatalysed cross-linked system. There are Health & Safety issues withorganotin catalysts used. However, UV curing is carried out at ambienttemperatures resulting in a substrate temperature of about 40° C whichdoes not result in any obvious alteration or distortion of the surfaceor mechanical properties of the substrate. This UV curing process can bedesigned with no temperature increase associated with the curing process(cold-cured systems) if required.

The invention may be carried into practice in various ways and someembodiments will now be illustrated in the following examples.

EXAMPLE 1

An EPDM extruded substrate was subjected to a pre-treatment consistingof the application of a solvent-based primer. A formulation X was madeup by mixing: % PUD (NeoRad R-440) 60.0 (40% solids) PUD (NeoRez R-600)20.0 (40% solids) Fluorinated polyether 10.0 Photoinitiator A or B (seebelow)  3.0 (equates to 40% solution) N-methyl-2-pyrrolidone (NMP)  4.0Wetting agents  3.0The formulation X was applied to an off-line sample of the substrate toa WFT (wet film thickness) of 15-20μ. Water was removed by heating for 2minutes at 120 to 150° C. UV curing was then effected by exposure to aUVA, UVB, UVC mercury lamp UV source for 1.0 second. The coating wasfound to have a DFF (day film thickness) of about 15μ. It was welladhered and resistant to abrasion while remaining flexible and of lowfriction.Photoinitiators

A. Coating contains 2 photoinitiators (Irgacure 184: Irgacure 819) in a[1:1] mixing (w/w/):

Irgacure 184

CAS 947-19-3

1-Hydroxy-cyclohexyl-phenyl-ketone

Irgacure 819CAS 162881-26-7BIS (2,4,6-trimethylbenzoyl)-phenylphosphineoxide

B. Coating contains one photoinitiator (Irgacure 2959):Irgacure 2959CAS 106797-53-91-[4(2-Hydroxyethoxy)-phenyl-2-hydroxy-2-methyl-1-propane-1-one

EXAMPLE 2

A TPE extrusion was pretreated by corona discharge on leaving theextruder and then sprayed with a formulation X (See Example 1 fordetails). The formulation was sprayed to a WFF of 15-20μ. The extrudedsubstrate had an inherent temperature of about 100° C. and so noseparate water removal was necessary. The sprayed substrate was exposedto the same UV source at a speed of 10 to 20 in/min. This produced afully cured coating with a DFr of about 15μ after less than 1 secondexposure to the UV source.

The UV Process

As UV light energy is emitted, it is absorbed by the photoinitiator inthe mobile coating (the “wet” coating film), causing it to fragment intoreactive species (free radicals). Free radicals react with theunsaturated compounds in the liquid formulation, resulting inpolymerisation.

Mechanism (applies to all photoinitiators)

Steps

1. A sealing system for automotives comprising a coating formulationapplied to a flexible thermoplastics extrusion wherein the coatingformulation comprises a UV curable resin.
 2. A sealing system as claimedin claim 1, wherein the extrusion is a Thermoplastic Elastomer (TPE)extrusion.
 3. A sealing system as claimed in claim 1, wherein theextrusion is a weatherstrip seal.
 4. A sealing system as claimed inclaim 1, wherein the resin is an aliphatic waterborne resin.
 5. Asealing system as claimed in claim 4, wherein the resin is apolyurethane dispersion (PUD).
 6. A sealing system as claimed in claim1, further comprising a solvent or dispersant for the resin.
 7. Asealing system as claimed in claim 6, wherein the solvent or dispersantis water.
 8. A sealing system as claimed in claim 1, wherein theformulation includes a friction-reducing agent.
 9. A sealing system asclaimed in claim 6, wherein the resin represents from 40 to 80 wt % ofthe formulation excluding the solvent or dispersant.
 10. The use of acoating formulation comprising a UV curable resin in coating a flexiblethermoplastics extrusion.
 11. The use as claimed in claim 10, whereinthe extrusion is a Thermoplastic Elastomer (TPE) extrusion.
 12. The useas claimed in claim 11, wherein the extrusion is a weatherstrip seal.13. A method of coating a flexible thermoplastics extrusion, the methodcomprising providing a coating formulation comprising a UV curableresin, applying the composition to a flexible extruded product andexposing the coated product to UV light of 200-400 nm.
 14. A coatingformulation for a flexible thermoplastics extrusion comprising a UVcurable waterborne resin and a water solvent or dispersant for saidresin.